1. Field of the Invention
The present invention relates to granular agrochemical compositions and to processes for producing such compositions. More particularly, it relates to controlled release agrochemical compositions having a first coating layer comprising a wax composition with a biologically active ingredient incorporated therein applied on the surface of a core material and having a second coating layer comprising a polymeric composition applied on the surface of the first coating layer and to processes for preparing such compositions.
2. Description of Related Art
Agrochemicals as referred to herein include biologically active ingredients/plant protection products such as insecticides, herbicides, fertilizers, growth regulators, pheromones, biostimulants, acaricides, miticides, nematocides, fungicides and the like. Such agrochemicals are well known and are in common usage for controlling pests and diseases and for promoting plant growth in agriculture . In practice, it is important to make a sufficient amount of such agrochemical or active ingredient available to the biological system in order to control pests or disease or to promote growth. Too much active ingredient, however, is inefficient and not desired because of environmental and economic concerns. Furthermore, higher amounts of active ingredient lead to increased risks of leaching to ground water or surface water. Higher amounts can also lead to phytotoxicity for the crop. Insufficient levels of active ingredients results in lack of control of the pest and increase the risk of resistance.
Thus, it is generally known that it is important to deliver the correct amount of active ingredient to the crop for control of the pest or disease and to promote growth over a given period of time. However, multiple applications of active ingredients becomes labor and cost intensive. With conventional applications of liquid or powder formulations, relatively high amounts of active ingredients are applied several times to assure control of pests over a longer period of time, typically 3-6 times for seasonal control, and users are exposed to the active ingredients during each application, which is undesirable.
When active ingredients are applied in granular form instead of by spraying or dusting, the risk of exposure to the active ingredient is more limited. After application of a granular pesticide the active ingredient is released to the soil under the influence of water. The release rate varies depending on the formulation of the granule. The granules can be divided into two categories. The first category releases the active ingredient quickly and has to be applied several times during the season. The second category releases the active ingredient over a period of time and provides control of pests during an extended period up to a whole season. To control pests over a longer period of time the concentration of active ingredient must be above the minimal effective level during the whole period. To maintain this effective concentration, the loss of active ingredient via leaching, degradation and uptake by the plant must be compensated. The rate of degradation and leaching depends on the active ingredient and the amount that is lost, is directly related to the concentration of the active ingredient in the soil. Thus high concentrations result in relatively more degradation and leaching.
In general, known controlled release granular active ingredients suffer serious limitations. They generally do not deliver the active ingredient to the biological system for periods of greater than about 30 days from the date of initial exposure to moisture and/or they do not completely release the active ingredient. The practical limitations of systems that release the active ingredient in less than about 30 days are that they must be periodically reapplied during the growing season resulting in additional cost. The limitations of systems which do not completely release the active ingredient in the desired period of time are related to efficiency. More active ingredient must be used to compensate for the portion which does not release effectively. This incurs additional cost to the user. Furthermore, the residual, unreleased active ingredient poses an environmental threat and can lead to biological resistance in the pest. Active ingredient that is not released cannot be used for controlling a pest or disease and will give undesirable residues of active ingredient. In the long run this can lead to build up of chemicals in soil and this is even less desirable. Without residues after the release period soil can be recycled without any risk for succeeding crop. The use of lower amounts of active ingredients and high efficiency are especially desired from an economical and environmental point of view.
A number of approaches have been taken heretofore in production of controlled release granular agrochemical compositions. For example, EP Patent 079668 discloses an encapsulated pesticide product wherein a granular core is coated with a pesticide and then a plurality of layers of a membrane like coating are applied over the pesticidal coat to enable controlled release of such pesticide over a period of time upon contact with water. However, the products disclosed in EP Patent 079668 are structurally distinct from the products of the present invention and, accordingly, disadvantageously fail to exhibit a controlled rate of release of the pesticide over a period greater than about 30 days from the date of initial exposure of the product to moisture in a manner such that essentially all of the pesticide coated on the core is released from the granular composition before the water soluble portion of the core material is released from the product as is achieved with the compositions of the present invention.
U.S. Pat. No. 6,682,751 discloses a granular pesticide comprising a core material coated with an inner polymer membrane formed in-situ on the core material with a pesticide applied to the inner polymer membrane and an outer controlled release polymer membrane formed in situ on the pesticide to permit controlled release. The pesticide may be incorporated in several “sandwich” layers. Again, the products of U.S. Pat. No. 6,682,751, are structurally different from the products of the present invention and fail to exhibit a controlled rate of release of the pesticide over a period greater than about 30 days from the date of initial exposure of the product to moisture in a manner such that essentially all of the pesticide coated on the core is released from the granular composition before the water soluble portion of the core material is released from the product.
U.S. Pat. No. 6,080,221 discloses the coating of porous surfaces of fertilizer particles with tenacious pesticide-resin solids to form attrition resistant fertilizer-pesticide combination particles. In this disclosure, the pesticide is dispersed in a resinoid matrix, which is subsequently bonded onto and into the fertilizer surface. Patent U.S. Pat. No. 4,971,796 describes another slow release granular product in which the pesticide is matrixed into the coating. The granule comprises one layer of proteinacious material or more layers of proteinacious material with intermediate spacing layers. The active ingredient is in the proteinacious layer and is released when this layer degrades. The release rate is changed by varying the cross linking or the thickness of the layer. The products of U.S. Pat. Nos. 6,080,221 and 4,971,796 fail to exhibit a controlled rate of release of the pesticide over a period greater than about 30 days from the date of initial exposure of the product to moisture in a manner such that essentially all of the pesticide coated on the core is released from the granular composition before the core material is released from the product.
U.S. Pat. Nos. 6,187,074 and 6,309,439 disclose a fertilizer coated with a carboxyl-carrying ethylene copolymer, the carboxyl-carrying ethylene copolymer being composed of 75%-90% by weight ethylene and from 10%-25% by weight of an alpha-olefinically unsaturated C3-C8 carboxylic acid. The coated fertilizer particles specifically do not contain any crop protection chemicals. Thus, the products disclosed in these patents fail to exhibit a controlled rate of release of the pesticide over a period greater than about 30 days from the date of initial exposure of the product to moisture in a manner such that essentially all of the pesticide coated on the core is released from the granular composition before the core material is released from the product.
U.S. Pat. No. 6,693,063 discloses products that are structurally distinct from the present compositions teaching wax microcapsules and wax dispersion of pesticides in the absence of a water soluble core material. Other encapsulated pesticides which do not include water soluble core materials are disclosed in Japanese Examined Patent Publication JP-B 5002/1989, JP-A 9304/1994 and JP-A 72805/1994.
Other pesticides displaying matrix release systems are disclosed in. U.S. Pat. No. 4,435,383 wherein solid controlled release pesticidal products are formed comprising an active ingredient incorporated in a homogeneous combination with a polymer by melting the polymer and mixing it with the active ingredient. During this process additional cross-linking agent are added. Another matrix based pesticide is disclosed in U.S. Pat. No. 5,516,520 wherein a pesticidally active ingredient is encapsulated in a starch-borax-urea matrix. The slow release from this matrix is limited to oil-soluble pesticides. The release rate is changed by varying the amount of urea.
EP Patent 0755370 discloses other matrix release products which are mixtures of a nitromethylene or related substances with fertilizers and glue. EP Patent 1063215 describes briquettes that slowly release active ingredients. The slow release is obtained via absorption or adsorption of the active ingredient onto solids with high surface area.
The matrix systems all demonstrate release mechanisms wherein the release of active ingredients from the matrix systems is via desorption from an absorped state or by diffusion and not by an osmotic (pump) release mechanism as employed herein. The release rate of such matrix systems depends on the concentration of the active ingredient in the system. Thus, the release rate of such granules decreases over time resulting in initial fast release of active ingredients which provides high amounts of active ingredient in the soil at the start, and a slow release at the end.
Other types of agrochemical products that can release an active ingredient over a period of time are biodegradable systems such as those disclosed in U.S. Pat. No. 4,062,855 wherein active ingredients are incorporated into a polymer that are released via biodegradation. U.S. Pat. No. 4,267,280 describes a product that has a biodegradable polymer system that contains the pesticide. It releases the pesticide depending on environmental conditions via hydrolyses or depolymerization.
A disadvantage of these biodegradable products is that the release of active ingredient depends on the speed of degradation of the polymer and this degradation depends on the activity of ambient microorganisms. The activity of the microorganisms can vary greatly depending on the soil type and local environmental conditions, types of microbes, pH, temperature, moisture and the like. Thus, the release rate of active ingredients varies and it is difficult to match the release precisely with the minimal required active ingredient concentrations.
Other coated granular pesticidal compositions are disclosed in International Patent Publication WO 02/05641 wherein a pesticidal composition is disclosed that can slowly release an active ingredient. That publication discloses the preparation of several granular materials with different numbers of coating layers or properties of the coating layers. Each of the granular materials has its own release profile. By blending the different granules they can obtain the desired release pattern of the product. The variation of release is purely based on coating properties and not on solubility of components in the formulation.
EP Patent 0966882 discloses a controlled release granular product wherein only single granules exhibit a delay of release after which the pesticide is released. Thus, after a period of time, a particular granule breaks open and delivers a portion of active ingredient to the environment. The release over a period of time is established by combining multiple ‘delayed-release’ granules, which all have different delay times. The granules themselves do not exhibit controlled release properties, only a delayed release.
EP Patent 1148107 discloses a coating procedure for granules with a low content of volatile substances. This coating procedure ensures that the release function of the granules does not change in two weeks time.
Another example of formulations of this general type is disclosed in International Patent Publication WO 99/07654 comprising encapsulated fertilizers with a polymeric envelope that contains a hormone (e.g. an auxin or cytokinine). The hormone is mixed with a monomer that form a polymeric envelope. Again, the products disclosed in this reference do not exhibit a controlled rate of release of the pesticide over a period greater than about 30 days from the date of initial exposure of the product to moisture in a manner such that essentially all of the pesticide coated on the core is released from the granular composition before the core material is released from the product.
In view of the benefits that can be derived from agrochemical compositions that provide controlled release of active ingredients including efficiency and economy of use of the active ingredients, the reduced environmental impact achieved, the ability to employ a single application of the composition for extended control of pests and diseases, reduction in user exposure to the compositions, it is clear that new, more technically advanced agrochemical products would be highly desirable. In particular, a desired objective is to provide agrochemical compositions that provide extended useful life with essentially complete release of an active ingredient occurring over a periods of greater than about 30 days from the date of initial exposure to moisture.
Thus, prior art agrochemical compositions have fallen short in providing desired functionality and the present invention is intended to overcome such problem by providing compositions which functionally demonstrate a controlled rate of release of the active ingredient over a period of time greater than about 30 days from the date of initial exposure of the compositions to moisture in a manner such that essentially all of the active ingredient coated on the core is released from the granular composition before the core material is released from the product.